This invention generally relates to a system for actively monitoring gear fatigue in a vehicle driveshaft while the vehicle is being driven.
Heavy vehicles, such as those operated in off-road environments, include a number of gears in the axle housing and planetary wheel ends (pinion, ring, planet and sun gears). Every rotation in combination with torque produces stresses on the gear teeth. These stress cycles cause the gears to fatigue. Gear combinations are selected for applications based on "typical" vehicle operation for the environment in which it will operate. The combination of driveshaft torque and driveshaft speed can be used to actively monitor gear stress and resulting fatigue caused by unexpected as well as "typical" vehicle operation.
Historically, gear fatigue has been estimated based on representative input factors. In other words, the gear life has been estimated based on expected vehicle operation. These representative values have been obtained from a combination of historical data, customer supplied usage criteria and empirical data.
The input factors used to determine the gear fatigue are the speed of rotation of the gear and the torque applied to the gear. These values are preferably used in combination with an algorithm to monitor unexpected torque/speed combinations as well as expected combinations that may impact the estimated fatigue performance of the gears. However, these calculations are not performed on-board during operation of the vehicle and thus are not representative of the cited gear damage.
It is important to note that many factors influence the fatigue performance of gears. Some factors include, but are not limited to, driver experience, driver abuse and operating environment, such as payloads and terrain. Using prior art representative samples, the gear performance in a particular application could fall short of expectations. Unexpected gear fatigue could cause unplanned operation down time and costly repairs. Alternatively, continuously monitoring the gear input factors could potentially prevent fatigue fracture and avoid unscheduled down time and costly repairs. Therefore, it is advantageous to monitor those factors that determine gear fatigue based on that vehicle's distinctive use history. Monitoring the gear performance optimizes the vehicle operation by decreasing down time and reducing unscheduled maintenance costs.
It is preferable to monitor gear fatigue so that a gear can be serviced or replaced at the time gear fatigue actually exceeds a threshold value. Consequentially, this proactive maintenance optimizes the performance of the vehicle and reduces maintenance costs in the long run. Gears will be serviced or replaced when they actually are in need.
Prior to this invention, there was no system available to actively determine the gear fatigue of a vehicle while the vehicle was in operation. This invention allows for a more accurate gear fatigue determination for each individual vehicle by continuously monitoring the input factors.